As well known, boilers have been used for heating rooms and supplying hot water at home or in public buildings. Generally, a boiler uses oil or gas as fuel and burns the fuel using a burner. Then, the boiler heats water using generated combustion heat during a procedure of combustion, and circulates the heated water to heat rooms or to supply hot water if necessary.
Generally, the boilers use a double pipe heat exchanger or a single pipe heat exchanger. The double pipe heat exchanger refers to one in which a hot water heat exchanging pipe is inserted into a heating water heat exchanger. The single pipe heat exchanger refers to one in which a hot water heat exchanger and a heating water heat exchanger are separately installed.
Since a boiler having the double pipe heat exchanger can be manufactured to be in a compact size in comparison with a boiler with the single pipe heat exchanger, it is possible to reduce a manufacturing cost of the boiler. Further, the boiler has a high heat efficiency.
FIG. 1 is a view showing a configuration of a conventional boiler having a double pipe heat exchanger.
In the conventional boiler, a burner 20 is disposed at a lower portion of a combustion chamber 10. A heat exchanger 30 is installed at an upper portion of the burner 20. Therefore, heat energy generated from the burner 20 is transferred to the heat exchanger 30 including pipes through which water generally flows.
While heating rooms, water stored in an expansion tank 40 of the boiler flows to the heat exchanger 30 by means of a circulation pump 60. Then, water heated by the heat exchanger 30 flows to a heating water line 50 through a heating water supply pipe 51 so as to heat rooms and sequentially circulates through the returned heating water pipe 52, which in turn returns to the expansion tank 40.
The conventional boiler with the double pipe heat exchanger has been designed in which a heating water line 50 is interrupted by means of a three-way valve 53 in order to rapidly supply hot water so that combustion heat of the burner 20 is transferred to the inner pipe 32 through the outer pipe 31 when a user uses the hot water.
Generally, if the temperature of heating water introduced into the heat exchanger 30 of the boiler is lower than a dew point of water vapor included in exhaust gas generated by the combustion in the burner 20, heating water is condensated.
Furthermore, hydrocarbon CnH2n+2 included in fuel for the boiler reacts with oxygen O2 and is converted into water vapor H2O and carbon dioxide CO2 while radiating heat. Then, exhaust gas is discharged outside through an exhaust port.
However, when water vapor mixed with the exhaust gas is cooled by means of an inlet pipe in which cold water or returned heating water is introduced, so that its temperature decreases below a dew point, the water vapor is converted into water H2O in a liquified state. Such condensated water reacts upon sulfur dioxide SO2 which is another component involved in the exhaust gas, and is converted into sulfuric acid H2 SO4 to cause corrosion around an inlet of a pipe for the heat exchanger.
FIG. 2 is a sectional view showing a configuration of a conventional double pipe heat exchanger.
As shown in FIG. 2 attached hereto, in the conventional double pipe heat exchanger, condensation concentrically occurs at an inlet 31a of the heat exchanger in which returned cold heating water causes corrosion of pipe around the inlet of the heat exchanger. Hence, there is a problem of the reduced lifetime of the heat exchanger and the boiler.